4.4 Effectiveness of a foot and mouth disease control programme

problems could potentially have occurred from initial vaccine quality and suitability, through vaccine storage, delivery and vaccination, vaccine coverage, induced immunity and the nature of the challenge, which might have been overwhelming owing to weight of infection, long post-vaccination interval or change in antigenic phenotype (Fig. 6).

The timing of outbreaks in relation to vaccination is a key consideration, as immunity takes time to develop and then wanes. Figure 7 shows a decision tree for this aspect of an investigation. A specific methodological approach utilising data collected in the course of outbreak investigations is given in Annex 4, based on experience of retrospective outbreak investigations in Turkey (27).

As already mentioned, and depending on the status of the country or zone, an FMD control programme (which may include vaccination) should be designed and implemented with a clear purpose at the outset. The same categories used in Chapter 3 to define target values for assessing immunity

Vaccination campaign applied after incubation time of outbreak (when first clinical signs were already present)

FMD virus was already present at time of vaccination campaign

Need to check with any epi-units being vaccinated subsequently that no FMD virus has been transferred leading to spread of infection

Stresses the need for SOP on biosecurity measures by vaccinators Vaccination campaign within incubation time of outbreak (1-30 days prior to date of first clinical signs)

There is direct time-association between vaccination activities and introduction of FMD virus as incubation period overlaps with date of vaccination

Need to check with epi-units vaccinated previously if clinical FMD was apparent or became apparent later

Vaccination campaign before incubation time of outbreak (more than 30 days prior to date of first clinical signs

There is apparent time association between vaccination and introduction of FMD virus, however, there is no overlap found between incubation period and date of vaccination

Result

Interpretation

Apparently, the vaccination has not lead to sufficient protection against FMD infection, which should be further investigated

Consideration

Need to check vaccine safety – is vaccine virus sufficiently inactivated? Conduct vaccine effectiveness study Are vaccinated animals better protected against clinical FMD compared with non-vaccinated animals? Need to check vaccine attributes: – matching between field virus and vaccine virus – potency of vaccine – shelf life – cold chain

Actions

Fig 7 Disease outbreak investigation Determining the relation between timing of the vaccination campaign and the incubation period of the outbreak

SOP: standard operating procedure